A light receiving section of a distance measuring device incorporated in a prior art automatic focusing camera will be described hereinbelow, by way of example, with reference to FIG. 9. In the drawing, a holder 20 is formed with a lens holding portion for holding a light receiving lens 21 at one end thereof and a substrate supporting frame 20a for supporting a first printed circuit board 22 at the other end thereof. An optical sensor (PSD) 23 of discrete parts for detecting distance is connected to the first printed circuit board 22, in such a way as to be aligned with an optical axis (the same as the geometric axis) 21a of the light receiving lens 21 through an opening 20b formed in the lens holder 20. One end of a flexible cable 23a (referred to hereinafter as FPC) is connected to the first circuit board 22. The other end of the flexible cable 23a is connected to a second printed circuit board 25 disposed within a cover 24. A distance measuring IC 26 is mounted on this second printed circuit board 25. Other electric parts (e.g., resistors, capacitors, etc.) 27 which constitute the measuring circuit are mounted on this second printed circuit board 25.
In the above-mentioned prior art distance measuring device, since the first printed circuit board 22 for mounting the optical sensor 23 and the second printed circuit board 25 for mounting the distance measuring IC 26 and other parts are both provided, the FPC 23a for connecting both the printed circuit boards 22 and 25 to each other and other members for supporting the second printed circuit board 25 in the holder 20 are inevitably required additionally, thus resulting in a problem in that the number of parts increases. In particular, since the optical sensor 23 and the IC 26 packaged as different discrete parts, respectively, are both used, it is difficult to mount the parts within a small space.
In addition, since the sizes and shapes of the second printed circuit board 25 and the cover 24 must be modified according to the models of cameras to facilitate mounting of these parts into a camera, there exists another problem in that these parts lack interchangeability. As described above, the prior art distance measuring device is poor in camera design freedom and it is difficult to reduce the size thereof.
As mentioned above, the optical sensor 23 and the distance measuring IC 26 packaged as discrete parts are used in order to make it possible for the optical sensor to receive incident light and to shield the IC from light to prevent erroneous operation due to light such as elimination of memory by incident light.
Furthermore, since the optical sensor 23 and the IC 26 are mounted a distance away from each other and connected through the FPC cable 23a, there exists a serious problem in that noise is easily superposed upon signals transmitted between both. Although this problem can be overcome to some extent by the use of a shielding structure, this countermeasure raises another problem in that the structure is further complicated.